1. Field of the Invention
The present invention relates to a water-borne complete inorganic alkali metal silicate composition and its aqueous solution, and a water-borne coat agent, its aqueous solution, a complete inorganic colored coating material and a binder for high temperature and heat resistance coating material of the same composition, as well as the method of using a water-borne complete inorganic alkali metal silicate compound, which are curable at normal temperature and by baking conditions, excellent in antifouling property, scratch resistance, weather resistance and chemical resistance, and capable of forming a clear coating film.
2. Description of the Related Art
Most of what are called as inorganic coating materials were formerly obtained by the Sol-Gel processing, or blending a water-borne mixture of an alkali metal silicate, such as sodium silicate, lithium silicate and potassium silicate, and a colloidal silica or silica powders, with an alkali alkyl siliconate used for the purpose of stabilizing the pot life by restraining gelation during the time course, and preventing cracks resulted from the polymerization contraction occurred during baking. In addition, there are available the aforementioned water-borne mixtures blended with an anionic surfactant or an organic solvent, and also mixed with a fluorinated coating material. However, it is difficult to say that these are genuinely inorganic coating materials since in terms of the hydrophilic property, their water contact angles are greater than 25 degrees due to the contamination of organic materials, resulting in no antifouling property.
Furthermore, concerning conventional organic/inorganic hybrid coating materials or coat agents based on an alkali metal silicate, it is necessary to bake them at 220° C. and higher. Especially in the case of the Sol-Gel processing, it is necessary to heat and bake them at 400° C. and higher in order to remove organic components, thereby causing them to change to yellow and making it impossible to form a clear film.
And also there is a water-borne inorganic coating material composition having a reduced amount of organic contents due to further improvement, which is known by the Japanese Examined Patent Application Publication No. H10-330646 with the title of the invention of “Water-borne inorganic coating material composition and coating film formation method thereof”. However, an alkali alkyl siliconate is blended in this coating material composition so that its hydrophilic property decreases, resulting in the lack of antifouling property. Moreover, as carbon in organic substances changes to yellow by heating during clear film formation due to the incorporation of organic substances, the subject coating material is inadequate in the formation of a clear film.
In the case of conventional water-borne inorganic coating materials/coat agents, unless organic substances are blended regardless of their amount, they become unusable in a relatively short period of time (within 3 months) during the retention period after being put on the market because of the silica content gradually turning into gel. Therefore it has been an inevitable way to blend anionic organic substances therein. Moreover, as the baking process is indispensable, they are required to be applied on the surface of objects to be coated and baked within plants before commercialization. As a result, the range of use has been extremely limited since it is not allowed to apply them to existing buildings, fixtures and furniture and the like on sight.
Then a superhydrophilic photocatalyst using titanium oxide capable of drying at normal temperature has been developed, attracting lots of attention at the present. However the aforementioned ambient drying photocatalyst does not have the photocatalytic effect in a place unaffected by ultraviolet rays and also the degrees of adhesion of titanium dioxide as a photocatalyst to a base material is low.
An alkali metal silicate compound has previously faced such problems that when the molar ratio of silica to alkali metal is small, efflorescence occurs, and conversely when the same ratio is increased, the solution during preservation period turns into gel. Therefore such water-borne inorganic coating materials/coat agents using the alkali metal silicate are blended with anionic organic substances without exception so that it is hard to say that they are easy-to-use to users from the viewpoints of the range of use, construction technique, etc.
Accordingly, the present invention has been made in view of the aforementioned circumstances, and it is an object of the present invention to provide a water-borne complete inorganic alkali metal silicate composition capable of solving the problem of gelation occurred in a preservation solution without using anionic organic substances, expanding the range of application dramatically, additionally solving the problem of efflorescence after coating, which is the biggest problem when the molar ratio of silica to alkali metal is low, and furthermore curing at normal temperature without baking, enabling the long-lasting effects.